1. Field of the Invention
The present invention relates to a self-propelled building machine, in particular a road cutting machine, having a machine frame and a running gear, which comprises at least one steerable front running gear, at least one rear left-hand running gear in the direction of working and at least one rear right-hand running gear in the direction of working. Additionally, the present invention relates to a process for operating such a building machine.
2. Description of the Prior Art
The above building machines comprise a working device having a working roller, which can be in the form of a milling or cutting roller. In known building machines, the operating depth of the working roller can be adjusted at least by adjusting the height of the rear running gears in the direction of working in relation to the machine frame resting on the ground in the direction of working.
When cutting into the ground, a road cutting machine is in general operated with the running gear in a raised position in relation to the machine frame, so that the cutting roller, at a given position of the cutting roller axis in relation to a reference plane, penetrates the ground. Under normal conditions, the reference plane is represented by the still uncut surface of the ground. For this reason, known building machines comprise devices to regulate the cutting depth in relation to the surface currently being worked by the machine.
However, in practice, cases can occur in which a machine has to rework a piece of ground that has already been partially cut. This can happen, for example, if a road has in the first instance undergone a large-scale cutting operation and subsequently has to undergo a small-scale cutting operation. If there are obstacles, for example a manhole cover, that prevent the ground from being worked with the large-scale cutting cutter, the cutting cutter has to be removed and replaced after the obstacle. This produces sections in which the ground has either been cut or has not been cut, with the result that there are differences in the heights of the individual sections and sudden gaps occur between these sections. The desired result then usually consists in adjusting the height of the covering to a level that corresponds to a section of ground that has already been cut. However, this cannot be done with existing known cutting depth adjustments.
The framework conditions described can, for example, lead to an operating condition in which the left hand running gear is lowered in relation to the frame of the machine, as it rests on a part of the ground that has already been cut, while the right-hand running gear is in a raised position, resting on a part of the ground that has not been cut with the result that although the machine is still effectively parallel to the ground surface, the axis of the cutting roller follows the direction of the reference plane. In this way, the non-cut section of the ground is adjusted to the required surface level, while the ground below is not subjected to any further treatment.
In the same way, operating situations can arise, in which the right-hand running gear is lowered in relation to the machine frame, while the left hand running gear is raised in relation to the machine frame. Furthermore, operating situations can arise in which both running gears are lowered in relation to the machine frame, so that the cutting roller is no longer in contact with the ground, because it is completely above the cut ground level.
These operating conditions cannot be addressed by the known cutting depth regulation systems, as in order to determine the working depth, all that needs to be done is to adjust the position of the working roller in relation to the surface that is currently being treated so that the ground that has already been cut is treated. This means that any necessary adjustments to the control systems of the known machines must be carried out manually by the user. This requires a high level of attention and concentration on the part of the user in addition to his other responsibilities, such as maintaining the cutting track